feat(foundry): add manual task owner change via UI dropdown

Add an owner dropdown to the Overview tab that lets users reassign task
ownership to any organization member. The owner's GitHub credentials are
used for git operations in the sandbox.

Full-stack implementation:
- Backend: changeTaskOwnerManually action on task actor, routed through
  org actor's changeWorkspaceTaskOwner action, with primaryUser schema
  columns on both task and org index tables
- Client: changeOwner method on workspace client (mock + remote)
- Frontend: owner dropdown in right sidebar Overview tab showing org
  members, with avatar and role display
- Shared: TaskWorkspaceChangeOwnerInput type and primaryUser fields on
  workspace snapshot types

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

foundry/packages/client/src/backend-client.ts

@@ -12,6 +12,7 @@ import type {
   TaskRecord,
   TaskSummary,
   TaskWorkspaceChangeModelInput,
+  TaskWorkspaceChangeOwnerInput,
   TaskWorkspaceCreateTaskInput,
   TaskWorkspaceCreateTaskResponse,
   TaskWorkspaceDiffInput,
@@ -110,6 +111,7 @@ interface OrganizationHandle {
   stopWorkspaceSession(input: TaskWorkspaceSessionInput & AuthSessionScopedInput): Promise<void>;
   closeWorkspaceSession(input: TaskWorkspaceSessionInput & AuthSessionScopedInput): Promise<void>;
   publishWorkspacePr(input: TaskWorkspaceSelectInput & AuthSessionScopedInput): Promise<void>;
+  changeWorkspaceTaskOwner(input: TaskWorkspaceChangeOwnerInput & AuthSessionScopedInput): Promise<void>;
   revertWorkspaceFile(input: TaskWorkspaceDiffInput & AuthSessionScopedInput): Promise<void>;
   adminReloadGithubOrganization(): Promise<void>;
   adminReloadGithubRepository(input: { repoId: string }): Promise<void>;
@@ -304,6 +306,7 @@ export interface BackendClient {
   stopWorkspaceSession(organizationId: string, input: TaskWorkspaceSessionInput): Promise<void>;
   closeWorkspaceSession(organizationId: string, input: TaskWorkspaceSessionInput): Promise<void>;
   publishWorkspacePr(organizationId: string, input: TaskWorkspaceSelectInput): Promise<void>;
+  changeWorkspaceTaskOwner(organizationId: string, input: TaskWorkspaceChangeOwnerInput): Promise<void>;
   revertWorkspaceFile(organizationId: string, input: TaskWorkspaceDiffInput): Promise<void>;
   adminReloadGithubOrganization(organizationId: string): Promise<void>;
   adminReloadGithubRepository(organizationId: string, repoId: string): Promise<void>;
@@ -1282,6 +1285,10 @@ export function createBackendClient(options: BackendClientOptions): BackendClien
       await (await organization(organizationId)).publishWorkspacePr(await withAuthSessionInput(input));
     },
 
+    async changeWorkspaceTaskOwner(organizationId: string, input: TaskWorkspaceChangeOwnerInput): Promise<void> {
+      await (await organization(organizationId)).changeWorkspaceTaskOwner(await withAuthSessionInput(input));
+    },
+
     async revertWorkspaceFile(organizationId: string, input: TaskWorkspaceDiffInput): Promise<void> {
       await (await organization(organizationId)).revertWorkspaceFile(await withAuthSessionInput(input));
     },

foundry/packages/client/src/mock/backend-client.ts

@@ -188,6 +188,8 @@ export function createMockBackendClient(defaultOrganizationId = "default"): Back
       unread: tab.unread,
       created: tab.created,
     })),
+    primaryUserLogin: null,
+    primaryUserAvatarUrl: null,
   });
 
   const buildTaskDetail = (task: TaskWorkspaceSnapshot["tasks"][number]): WorkspaceTaskDetail => ({
@@ -750,6 +752,15 @@ export function createMockBackendClient(defaultOrganizationId = "default"): Back
       emitTaskUpdate(input.taskId);
     },
 
+    async changeWorkspaceTaskOwner(
+      _organizationId: string,
+      input: { repoId: string; taskId: string; targetUserId: string; targetUserName: string; targetUserEmail: string },
+    ): Promise<void> {
+      await workspace.changeOwner(input);
+      emitOrganizationSnapshot();
+      emitTaskUpdate(input.taskId);
+    },
+
     async revertWorkspaceFile(_organizationId: string, input: TaskWorkspaceDiffInput): Promise<void> {
       await workspace.revertFile(input);
       emitOrganizationSnapshot();

foundry/packages/client/src/mock/workspace-client.ts

@@ -349,7 +349,10 @@ class MockWorkspaceStore implements TaskWorkspaceClient {
 
       return {
         ...currentTask,
-        activeSessionId: currentTask.activeSessionId === input.sessionId ? (currentTask.sessions.find((candidate) => candidate.id !== input.sessionId)?.id ?? null) : currentTask.activeSessionId,
+        activeSessionId:
+          currentTask.activeSessionId === input.sessionId
+            ? (currentTask.sessions.find((candidate) => candidate.id !== input.sessionId)?.id ?? null)
+            : currentTask.activeSessionId,
         sessions: currentTask.sessions.filter((candidate) => candidate.id !== input.sessionId),
       };
     });
@@ -396,6 +399,14 @@ class MockWorkspaceStore implements TaskWorkspaceClient {
     }));
   }
 
+  async changeOwner(input: { repoId: string; taskId: string; targetUserId: string; targetUserName: string; targetUserEmail: string }): Promise<void> {
+    this.updateTask(input.taskId, (currentTask) => ({
+      ...currentTask,
+      primaryUserLogin: input.targetUserName,
+      primaryUserAvatarUrl: null,
+    }));
+  }
+
   private updateState(updater: (current: TaskWorkspaceSnapshot) => TaskWorkspaceSnapshot): void {
     const nextSnapshot = updater(this.snapshot);
     this.snapshot = {

foundry/packages/client/src/remote/workspace-client.ts

@@ -1,6 +1,7 @@
 import type {
   TaskWorkspaceAddSessionResponse,
   TaskWorkspaceChangeModelInput,
+  TaskWorkspaceChangeOwnerInput,
   TaskWorkspaceCreateTaskInput,
   TaskWorkspaceCreateTaskResponse,
   TaskWorkspaceDiffInput,
@@ -140,6 +141,11 @@ class RemoteWorkspaceStore implements TaskWorkspaceClient {
     await this.refresh();
   }
 
+  async changeOwner(input: TaskWorkspaceChangeOwnerInput): Promise<void> {
+    await this.backend.changeWorkspaceTaskOwner(this.organizationId, input);
+    await this.refresh();
+  }
+
   private ensureStarted(): void {
     if (!this.unsubscribeWorkspace) {
       this.unsubscribeWorkspace = this.backend.subscribeWorkspace(this.organizationId, () => {

foundry/packages/client/src/workspace-client.ts

@@ -1,6 +1,7 @@
 import type {
   TaskWorkspaceAddSessionResponse,
   TaskWorkspaceChangeModelInput,
+  TaskWorkspaceChangeOwnerInput,
   TaskWorkspaceCreateTaskInput,
   TaskWorkspaceCreateTaskResponse,
   TaskWorkspaceDiffInput,
@@ -43,6 +44,7 @@ export interface TaskWorkspaceClient {
   closeSession(input: TaskWorkspaceSessionInput): Promise<void>;
   addSession(input: TaskWorkspaceSelectInput): Promise<TaskWorkspaceAddSessionResponse>;
   changeModel(input: TaskWorkspaceChangeModelInput): Promise<void>;
+  changeOwner(input: TaskWorkspaceChangeOwnerInput): Promise<void>;
 }
 
 export function createTaskWorkspaceClient(options: CreateTaskWorkspaceClientOptions): TaskWorkspaceClient {

foundry/packages/client/test/subscription-manager.test.ts

@@ -77,6 +77,8 @@ function organizationSnapshot(): OrganizationSummarySnapshot {
         pullRequest: null,
         activeSessionId: null,
         sessionsSummary: [],
+        primaryUserLogin: null,
+        primaryUserAvatarUrl: null,
       },
     ],
   };
@@ -159,6 +161,8 @@ describe("RemoteSubscriptionManager", () => {
             pullRequest: null,
             activeSessionId: null,
             sessionsSummary: [],
+            primaryUserLogin: null,
+            primaryUserAvatarUrl: null,
           },
         ],
       },